One technique for fabricating three-dimensional objects is to deposit layers of dry powder and bind selected portions of the layers together. A common problem faced when creating three-dimensional objects from dry powder is that powder particles in the surface layer are easily displaced by activities required to apply binder to the powder.
One significant cause of the dry powder disturbance is kinetic energy of the binder drops hitting the surface layer at a speed usually in the range of 5-20 m/sec. On impact, binder drops create small “craters” on the non-bound powder surface. This “cratering” manifests itself in increased surface roughness of the printed object and, hence, degrades the object quality. In some extreme cases (low mass/density powder particles, heavy and fast drops) the “cratering” makes creation of a smooth surface finish very difficult to achieve.
Another common cause of powder disturbance is air turbulence related to fast motion of print members, such as printheads and carriages, in close proximity to the surface of the dry powder. Build powder easily moves or becomes airborne, resulting in increased print member contamination and in reduced object quality. When airborne powder settles and builds up on print members, their ability to accurately apply binder fluid is reduced or eliminated. Since accurate and consistent placement of binder fluid is required to provide structure and strength to the object being built, reduced print member performance may result in reduced object structure and strength. Additionally, for objects where color is applied, poor appearance may result from even a small number of blocked nozzles on one print member.